A practical device of this kind is used as a so called “limited slip coupling” in a four-wheel-driven car for transmitting force for example from the driving forward axle of the car to its driven rear axle. In such a case, the coupling is arranged in the longitudinal drive shaft between the forward and rear axles.
The coupling is based on the principle that when there is a rotational speed differential between the two shaft members in the coupling, the differential pump will create a hydraulic flow which—moderated by the electrically controlled valve—will be transmitted to the clutch for counteracting the rotational speed differential.
A typical example of such a limited slip coupling is shown in WO 97/04245, to which reference is made for further information.
A possible drawback with the coupling shown therein and referred to above is that it may in certain cases be desirable to transmit a certain moment already when the vehicle or car stands still—a so called “lockup from stationary”. As the design so far described is dependent for its function on a certain rotational speed differential this is not possible.
The main object of the invention is thus to modify the device or coupling as so far described to enable a “lockup from stationary”.